This application claims the benefit of Korean Patent Application No. P99-18569, filed on May 21, 1999, which is hereby incorporated by reference.
1. Field of the Invention
This invention relates to a liquid crystal display (LCD) and more particularly, to an LCD that has stronger adhesion between a tape carrier package (TCP) and an LCD panel having an organic insulating layer, and a method for manufacturing the same.
2. Description of the Related Art
Generally, an LCD controls the light transmissivity of liquid crystal cells in response to a video signal, thereby displaying a picture that reflects the video signal that is transmitted to the liquid crystal panel in which liquid crystal cells are arranged in a matrix pattern. To achieve this result, the LCD includes drive integrated circuits (ICs) for driving the liquid crystal cells that are arranged in the matrix pattern on the liquid crystal panel. The drive ICs are manufactured in chip form. The drive IC chips are loaded onto the TCP when the LCD is implemented in a Tape Automated Bonding (TAB) system. Alternatively, if the LCD is implemented in a Chips On Glass (COG) system, the drive IC chips are mounted on the liquid crystal panel. The drive IC chips that are implemented in the COG system are electrically connected to a pad portion on the liquid crystal panel by the TCP.
FIG. 1 shows a surface of a conventional liquid crystal panel. The liquid crystal panel 2 has a structure that includes a lower substrate 4 and an upper too, substrate 6, which are bonded so as to oppose each other. The liquid crystal panel 2 also includes a display portion 8 that is provided with liquid crystal cells arranged in a matrix, and a gate pad portion 12 and a data pad portion 14 arranged such that each is connected between the drive IC chips (not shown) and the display portion 8. The display portion 8 includes gate lines and data lines arranged on the lower substrate 4 such that they intersect each other, thin film transistors for switching the liquid crystal cells located at the intersections of the gate and data lines, and pixel electrodes that are each connected to the thin film transistors for driving the liquid crystal cells. Also, the display portion 8 has color filters separated by a black matrix on the upper substrate 6 that are the size of a cell region, and a transparent common electrode coated on the surface of the color filters. The lower substrate 4 and the upper substrate 6 are separated from each other by spacers to define a cell gap so that the cell gap. can be filled with liquid crystal material. Also, the lower substrate 4 and the upper substrate 6 are bonded to each other by a sealing material 10 that surrounds the display portion 8. The gate pad portion 12 and the data pad portion 14 are provided at the edges of the lower substrate 4 which are not overlapped with the upper substrate 6. The gate pad portion 12 applies a gate driving signal from the gate drive IC chips, which are included in the drive IC chips, to the gate lines of the display portion 8. The data pad portion 14 transmits a video signal from the data drive IC chips, which are included in the drive IC chips, to the data lines of the display portion 8.
The liquid crystal panel 2 having the above-described structure uses a protective layer which is disposed on the entire surface of the lower substrate 4 to protect the pixel electrodes and the thin film transistors. The conventional protective layer is an inorganic layer made from SiNx, SiOx and other similar materials. In order to minimize the coupling effect caused by parasitic capacitance, the pixel electrodes and the data lines that are opposite each other have the inorganic protective layer as their center, and must be apart from each other by a constant distance, for example, about 3 to 5 xcexcm. This is required because the inorganic protective layer has a high dielectric constant. Due to this, the pixel electrode, which determines the aperture ratio, must be small in size.
Conventionally, to make the pixel electrode bigger so that the aperture ratio is greater, an organic material such as benzocyclobutene (BCB), which has a low dielectric constant, is used as the protective layer. For exarmple, in U.S. Pat. No. 5,798,812, there is provided an organic insulating film that covers the pixel area. and the pad area portions of the LCD. Because the organic protective layer has a dielectric constant lower than that of the inorganic protective layer by about 2.7, the pixel electrode can be overlapped with the data line. Thus, the pixel electrode can be enlarged by the amount of overlap between the pixel electrode and the data line so that the aperture ratio of the liquid crystal cell is increased.
The LCD of the TAB system allows the TCP that mounts the drive IC chips to contact the gate and data pad portions. The TAB process forces the TCP to be repeatedly bonded to and then separated from the data and gate pad portions of the liquid crystal panel. In order to prevent the metallic electrodes that are used as the data pads from being damaged due to the repeated bonding and separation between the TCP and the data pad portion of the liquid crystal panel, the data pads that are included in the data pad portion and defined by metallic electrodes are connected to the TCP via transparent electrodes. However, the organic protective layer is weakly bonded with the gate insulating layer and therefore separates easily from the gate insulating layer. As a result, the transparent electrode on the organic protective layer is also easily separated. This problem will be described hereinbelow with reference to FIGS. 2 to 5B.
FIG. 2 is a detailed view of a part of the gate pad portion 12 of FIG. 1. FIG. 3A is a cross-sectional view representing the gate pad portion taken along the IIIA-IIIAxe2x80x2 line as shown in FIG. 2. FIG. 3B is a cross-sectional view of the gate pad portion 12 taken along the IIIB-IIIBxe2x80x2 line as shown in FIG. 2. Referring to FIGS. 2, 3A and 3B, the gate pads 16 are provided on a lower glass substrate 22 together with the gate lines that are included in the display portion all at the same time. A gate insulating layer 24 and an organic protective layer 26 are sequentially disposed on the entire surface of the lower glass substrate 22 having the gate pads 16 thereon. The gate insulating layer 24 and the organic protective layer 26 are patterned so as to form holes 18 at each of the gate pads 16. The holes 18 that are located at each gate pad 16 allow the gate pads 16 to be exposed. Transparent electrode patterns 20 are then formed on the organic protective layer 26 such that the transparent electrode patterns 20 are each connected to the corresponding gate pad 16 through the corresponding hole 18.
Note that the organic protective layer 26 is weakly bonded with the gate insulating layer 24 and so is separated easily from the gate insulating layer 24 when the TCP is separated from the gate pad portion 12 on the liquid crystal panel. Also, the adhesion between the organic protective layer 26 and the gate insulating layer 24 is further weakened by the holes 18 that are defined in the organic protective layer 26 and the gate insulating layer 24 so that almost all of the organic protective layer 26 becomes separated when the TCP is separated from the gate pad portion 12.
Therefore, the gate pad portion 12 does not have a uniform surface due to the separation of the organic protective layer 26. Because of this, the TCP becomes weakly bonded with the gate pad portion 12 when it is re-bonded with the gate pad portion 12 so as to decrease the connection area causing increased resistance. Further, the transparent electrode 20 is also separated from the gate pad portion 12 when the organic protective layer 26 becomes separated and exposes the gate pads 16. Thus, the gate pads 16 are easily damaged or oxidized.
FIG. 4 is a detail view of a part of the data pad portion 14 of FIG. 1. FIG. 5A is a cross-sectional view representing the data pad portion 14 taken along the VA-VAxe2x80x2 line of FIG. 4, and FIG. 5B is a cross-sectional view of the data pad portion 14 taken along the VB-VBxe2x80x2 line of FIG. 4. Data pads 28, as shown in FIGS. 4, 5A and 5B, are provided on the gate insulating layer 24 of a lower glass substrate 22 together with the data lines (not shown) all at the same time. A semiconductor layer 30 under the data pad 28 is extended to the data line. The organic protective layer 26 is disposed on the entire surface of the gate insulating layer 24 having the data pads thereon. The organic protective layer 26 is patterned so as to define holes 18 at each of the data pads 28. The holes 18 defined at each of the data pads 28 allow the data pads 28 to be exposed. Transparent electrode patterns 20 are defined on the organic protective layer 26 such that the electrode patterns 20 are each connected to the corresponding data pad 28 through the corresponding hole 18.
Note that the organic protective layer 26 is weakly bonded with the gate insulating layer 24 and therefore separates easily from the gate insulating layer 24 when the TCP is separated from the data pad portion 14 on the liquid crystal panel. Also, the adhesion between the organic protective layer 26 and gate insulating layer 24 is further weakened by the holes 18 that are defined on the organic protective layer 26 so that almost all of organic protective layer 26 becomes removed during this process.
Therefore, the data pad portion 14 has a surface that is non-uniform due to the separation of the organic protective layer 26. Because of this, the TCP becomes weakly bonded with the data pad portion 14 when it is re-bonded with the data pad portion 14 so as to decrease the connection area causing increased resistance. Further, the transparent electrode 20 is also separated from the data pad portion 14 along with the organic protective layer 26 so that the data pads 28 become exposed. Thus, the data pads 28 are easily damaged or oxidized.
To overcome the problems described above, preferred embodiments of the present invention provide an LCD that has stronger adhesion between the TCP and a liquid crystal panel while providing a high aperture ratio by using an organic insulating layer.
A preferred embodiment of the present invention includes a substrate, electrode pads on the substrate, transparent electrodes arranged on the electrode pads, and a semiconductor layer disposed between the substrate and the transparent electrodes, wherein the semiconductor layer is in contact with the transparent electrodes.
Another preferred embodiment of the present invention includes a glass substrate, a gate insulating layer on the glass substrate, electrode pads on the glass substrate, transparent electrodes on the electrode pads for protecting the electrode pads, a semiconductor layer on the gate insulating layer for preventing an etching of a gate insulating layer that is in contact with the electrode pads, and wherein the semiconductor layer is in contact with the transparent electrodes.
According to another preferred embodiment of the present invention a method for manufacturing an LCD includes the steps of providing a glass substrate, forming gate pads on the glass substrate, overlaying a gate insulating layer on the entire surface of the glass substrate and forming holes exposing the gate pads, forming data pads on the gate insulating layer, disposing a semiconductor layer on the gate insulating layer, wherein the semiconductor layer is at least partially beneath the data pads, and wherein the semiconductor layer is at least partially overlapped with the the gate pads, coating an organic protective layer on the entire surface of the glass substrate, sequentially etching the organic protective layer and the gate insulating layer in an area of the gate pads and the data pads, wherein the organic protective layer is removed from the area of the gate and data pads, and forming transparent electrodes on the data and gate pads for protecting the data and gate pads.
Thus, the present invention described herein makes possible the advantages of having stronger adhesion between the TCP and the pad portions of a liquid crystal panel while improving the aperture ratio of the LCD.
Other features, elements and advantages will be described in detail below with reference to preferred embodiments of the present invention and the attached drawings.